Near-Fault Seismic Vulnerability Assessment of Corrosion Inflicted 8-Storey Steel Moment Resisting Frame

Special steel moment resisting frames (SMRFs) are competent ductile lateral force resisting system to shield the structures against adverse seismic effects. They are identified by moment taking beam-column connections dimensioned based on strong column-weak beam capacity limit stipulations. The desired ductile seismic response of the SMRFs are ensured by virtue of the near end provided reduced beam sections (RBSs) along with the special beam and column cross-section detailing requirements. The reasonable post yield strength and stiffness of the SMRFs instigated primarily from the beam yielding at RBSs helps to reduce the seismic drift demand and hence the resulting losses in the framed structures. Being made with steel material, under extreme atmospheric conditions, the SMRFs are also susceptible to time-dependent corrosion effects. The corrosive action on SMRFs eventually reduces the component cross-sectional area, material yield strength and the system ductility. This may negatively alter the seismic response of SMRFs compared to the uncorroded case causing unforeseen and unintended seismic losses. The present investigation attempts to evaluate the seismic behaviour of a 50-year corrosion inflicted 8-storey 3-bay (8S3B) SMRF designed according to latest US code provisions (ASCE 7-22). The adopted study SMRF numerical models (both corroded and uncorroded) are generated in the finite element based OpenSees framework and the earthquake response is assessed in terms of nonlinear time history (NTH) based incremental dynamic analysis (IDA). For this, a set of near-fault (NF) earthquake records used in the past studies are used and the SMRF responses are obtained in terms of maximum inter-storey drift ratio (IDR) and residual storey drift ratio (RDR). Successively, the obtained IDA data are used to develop the fragility curves corresponding to different damage states for both the corroded and uncorroded cases and the NF seismic vulnerability of the SMRF is assessed for the accounted scenario.